The goals of this research are to more fully understand the basis for individual differences in cardiovascular reactivity to stress and to assess whether particularly hyperreactive individuals are at increased risk for the development of hypertension. The proposed strategy is to conduct initial laboratory studies to provide a detailed evaluation of behavioral and physiological characteristics of a group of young men (aged 18-25) with normal or elevated casual blood pressure. A follow-up study will then assess long-term aspects of blood pressure regulation and attempt to relate these to initial test characteristics. Initial testing will involve exposure to standard laboratory stressors such as a reaction-time shock-avoidance task, mental arithmetic and cold pressor. The opportunity for greater behavioral flexibility will also be introduced by presenting choice of task difficulty, as well as including a speech evaluation stressor, with the aim of assessing whether this may reveal a closer link between reactivity and personality traits (e.g., Type Alpha). Non-invasive measurements will include blood pressure and cardiac output, permitting the derivation of systemic vascular resistance responses and the hemodynamic basis of pressor reactivity. Invasive procedures include venous blood sampling for plasma catecholamines and pharmacological manipulations designed to permit the evaluation of cardiovascular alpha- and beta- adrenergic receptor sensitivities. The data collected from these studies will be analyzed with the general aim of assessing the relative contributions of behavioral characteristics, sympathetic nervous system activation and target adrenoceptor sensitivities in determining individual differences in cardiovascular reactivity to stress. At follow-up, 2-3 years later, catecholamine responses and adrenergic receptor sensitivities will be re-evaluated in relation to the long term stability of stress reactivity and changes in resting blood pressure. Together, these studies are aimed at understanding the mechanisms by which behavior may play a role in the etiology of hypertension.